1. Field of the Invention
The present invention relates to an oscillation circuit used in high-frequency circuits of various communication equipment such as BS tuner, digital TV tuner and cellular telephone.
2. Description of the Related Art
FIG. 12 shows an example of circuit diagram of an oscillation circuit having differential configuration of the prior art. This oscillation circuit has such a configuration as one terminal of a current source I1N is connected to a power terminal to which a power voltage VCC is applied, and one terminal each of inductance elements L1, L2 is connected to other terminal of the current source I1N. The other terminals of the inductors L1, L2 are connected to anode terminals of varactor diodes C11, C21 used as adjustable capacitance elements, and cathode terminals of the varactor diodes C11, C21 are connected with each other while a frequency tuning voltage VTX is applied thereto. The inductance elements L1, L2 and the varactor diodes C11, C21 constitute an LC resonance circuit RC3.
Junction of the inductance element L1 and the varactor diode C11 is connected to the collector of a bipolar transistor (hereafter referred to as transistor) TIN1 which is a 3-terminal active element, while the emitter of the transistor TIN1 is grounded via an emitter resistor RE1. Junction of the inductance element L2 and the varactor diode C21 is connected to the collector of a transistor TIN2 which is a 3-terminal active element, while the emitter of the transistor TIN2 is grounded via an emitter resistor RE2. The base of the transistor TIN1 is connected to the collector of the transistor TIN2, and the base of the transistor TIN2 is connected to the collector of the transistor TIN1.
Junction of the inductance element L1, the varactor diode C11, and the transistor TIN1 is connected to the base of the transistor QP1 that constitutes an emitter follower circuit. Collector of the transistor QP1 is connected to a power terminal, while the emitter is grounded via a current source IP1 and is, at the same time, connected to the base of a transistor QP2 that constitutes the emitter follower circuit. Collector of the transistor QP2 is connected to the power terminal, while the emitter is grounded via a current source IP2, so that one of oscillation outputs VOUT (+) is obtained at the emitter of the transistor QP2.
Junction of the inductance element L2, the varactor diode C21, and the transistor TIN2 is connected to the base of the transistor QN1 that constitutes an emitter follower circuit. Collector of the transistor QN1 is connected to a power terminal, while the emitter is grounded via a current source IN1 and is, at the same time, connected to the base of a transistor QN2 that constitutes the emitter follower circuit. Collector of the transistor QN2 is connected to the power terminal, while the emitter is grounded via the current source IN2, so that the other oscillation outputs VOUT (xe2x88x92) is obtained at the emitter of the transistor QN2.
In the oscillation circuit having such a constitution as described above, the inductance elements L1, L2 and the varactor diodes C11, C21 constitute an LC parallel resonance circuit (hereafter abbreviated as LC resonance circuit), while a resonance signal of the LC resonance circuit that is connected as a load to the collectors of the transistors TIN1, TIN2 is fed to the bases of the transistors TIN1, TIN2 in positive feedback, thereby carrying out oscillation operation.
In this oscillation circuit, LC resonance frequency is changed and the oscillation frequency is accordingly changed by varying the voltage VTX applied to the cathode terminals of the varactor diodes C11, C21 thereby varying the capacitances of the varactor diodes C11, C21.
In the oscillation circuit of the prior art described above, the inductance elements L1, L2 of the LC resonance circuit includes not only pure inductance component but also a series resistive component. In such an oscillation circuit, when the resonance frequency is changed in order to change the oscillation frequency, Q factor of oscillation also varies in concert therewith, thus resulting in such a problem that the oscillation output level changes and stable oscillation cannot be maintained.
Also because the varactor diodes C11, C21 are used as adjustable capacitance elements in the LC resonance circuit for the tuning of oscillation frequency, the tunable range of the oscillation frequency is determined by the adjustable range of capacitances of the varactor diodes C11, C21. Thus since the varactor diodes C11, C21 do not have large adjustable range of capacitances due to the characteristics thereof, it has been difficult to achieve oscillation over a large frequency range.
An object of the present invention is to provide an oscillation circuit that is capable of maintaining stable oscillation when the oscillation frequency is changed.
Another object of the present invention is to provide an oscillation circuit that is capable of making stable oscillation over a large range of frequencies.
An oscillation circuit of the first invention comprises a 3-terminal active element and an LC resonance circuit, the LC resonance circuit being connected with two terminals of the 3-terminal active element and output signal of the 3-terminal active element being fed back to the input terminal of the 3-terminal active element, wherein a voltage-current converter circuit that converts the voltage across the LC resonance circuit to a current and a current path for supplying the output current of the voltage-current converter circuit to the LC resonance circuit are provided. The voltage-current converter circuit and the current path function as Q-factor tuning voltage-current converter circuit that tunes the Q factor of the LC resonance circuit.
An oscillation circuit of the second invention comprises a pair of transistors that supply signals to bases or gates of a plurality of transistors of which emitters or sources are connected with each other and output a signal from the collector or the drain thereof, and a plurality of LC resonance circuits with one end each thereof being ac-grounded, wherein the other ends of the LC resonance circuits are connected to same type terminals of the transistors that constitute the transistor pair, and the signal from the collector or drain of each transistor of the transistor pair is fed back to the base or gate of the other transistor.
The oscillation circuit is characterized in that the voltage-current converter circuit that converts the voltage across the LC resonance circuit into a current and the current path for supplying the output current of the voltage-current converter circuit to the LC resonance circuit are provided. The voltage-current converter circuit and the current path function as Q-factor tuning voltage-current converter circuit that tunes the Q factor of the LC resonance circuit.
With these constitutions, when the oscillation frequency is changed by changing the resonance frequency of the LC resonance circuit, C/N characteristic deteriorates because the resistive component included in the LC resonance circuit causes the Q factor of the LC resonance circuit to change in concert therewith, although the change in the Q factor of the LC resonance circuit can be compensated for by means of the Q-factor tuning voltage-current converter circuit. As a result, it is made possible to stabilize the oscillation output level and the C/N characteristic when the oscillation frequency is changed.
The LC resonance circuit may be provided, for example, in the following two constitutions. An LC resonance circuit of the first constitution comprises an LC resonance main circuit consisting of an inductance element and a capacitance element, a current sensing resistor provided in series with the capacitance element and a frequency tuning voltage-current converter circuit that converts a voltage across the current sensing resistor into a current and outputs the current, wherein the resonance frequency is changed by feeding back the output current of the frequency tuning voltage-current converter circuit to the LC resonance main circuit.
An LC resonance circuit of the second constitution comprises of an inductance element and a capacitance element, wherein the capacitance element is constituted from a varactor diode and the oscillation frequency of the oscillation circuit is changed in accordance with a voltage applied from the outside to the varactor diode.
In the first constitution, since the resonance frequency of the LC resonance circuit is changed by means of the frequency tuning voltage-current converter circuit, tunable range of the resonance frequency is not limited, for example, within the adjustable range of the capacitance of the capacitance element, and the resonance frequency of the LC resonance circuit can be changed over a large range of frequencies. Thus it is made possible to oscillate over a large frequency range. Moreover, it is made possible to maintain oscillation with stable output power and C/N characteristic over a large frequency range, together with Q tuning by means of the Q-factor tuning voltage-current converter circuit.
In the second constitution, the resonance frequency can be changed with such a simple constitution that only adjusts the voltage applied to the varactor diode. Moreover, it is made possible to maintain oscillation with stable output power and C/N characteristic regardless of changes in the frequency, together with Q tuning by means of the Q-factor tuning voltage-current converter circuit.
An oscillation circuit of the third invention comprises a main portion of the oscillation circuit, second and third transistor pairs, second and third current sources, first and second resistors and connecting means.
The main portion of oscillation circuit comprises the first transistor pair, an LC resonance circuit and the first current source.
Emitters of the transistors of the first transistor pair are connected with each other, and the base of each transistor is connected to the collector of the other transistor. The LC resonance circuit is connected with the collectors of the transistors of the first transistor pair. The first current source is connected to the emitters of the transistors of the first transistor pair. The main portion of oscillation circuit outputs the oscillation signal from the collectors of the transistors of the first transistor pair.
Emitters of the transistors of the second transistor pair are connected with each other, and emitters of the transistors of the third transistor pair are connected with each other
The second current source is connected to the emitters of the transistors of the second transistor pair, and the third current source is connected to the emitters of the transistors of the third transistor pair.
The first resistor is connected, on one terminal thereof, to the junction of the collector and the base of one of the transistors of the second transistor pair and the base of one of the transistors of the third transistor pair.
The second resistor is connected, on one terminal thereof, to the junction of the collector and the base of the other transistor of the second transistor pair and the base of the other transistor of the third transistor pair.
The connecting means connects the other terminals of the first and the second resistors and the collectors of the transistors of the first transistor pair, respectively.
This constitution makes it possible to change the Q factor of the oscillation signal of the main portion of oscillation circuit in accordance with the current ratio between the second and third current sources.
In the oscillation circuit having the constitution of the third invention, the LC resonance circuit is constituted from, for example, an inductance element and a varactor diode.
Capacitance of the varactor diode is changed by applying a voltage from the outside to the varactor diode, thereby changing the oscillation frequency of the oscillation circuit that includes the capacitance as a constituent element.
An oscillation circuit of the fourth invention comprises a main portion of oscillation circuit, a resistor, the second pair of transistors and the second current source.
The main portion of oscillation circuit comprises the first pair of transistors, the LC resonance circuit and the first current source.
Emitters of the transistors of the first transistor pair are connected with each other, and the base of each transistor is connected with the collector of the other transistor. The LC resonance circuit is connected with the collectors of the transistors of the first transistor pair. The first current source is connected to the emitters of the transistors of the first transistor pair. The main portion of oscillation circuit outputs an oscillation signal at the collectors of the transistors of the first transistor pair.
The resistor senses the current flowing in the element that constitutes the LC resonance circuit.
Emitters of the transistors of the second transistor pair are connected with each other, and bases of the transistors are connected to the respective terminals of the resistor, while the collectors of the transistors are connected to the collectors of the transistors of the first transistor pair.
The second current source is connected to the emitters of the transistors of the second transistor pair.
This constitution makes it possible to differentiate the oscillation frequency of the main portion of oscillation circuit in accordance with the current ratio between the first and second current sources.
Now the capability to differentiate the oscillation frequency will be described below. Magnitude of current flowing in the capacitance element can be sensed by connecting the resistor in series with the capacitance element that constitutes the LC resonance circuit. The current that is sensed is amplified by the second transistor pair and is fed to the collector of the first transistor in current feedback, so that the value of capacitance element that constitutes the LC resonance circuit is equivalently differentiated, thereby making it possible to differentiate the oscillation frequency.
An oscillation circuit of the fifth invention comprises an LC resonance circuit having a capacitance element and an inductance element and a 3-terminal active element, while the LC resonance circuit is connected with two terminals of the 3-terminal active element and output signal of the 3-terminal active element is fedback to the input terminal of the 3-terminal active element, wherein a voltage-current converter circuit that converts the voltage across the LC resonance circuit to a current, a first current path for supplying the output current of the voltage-current converter circuit to the LC resonance circuit, an amplifier circuit that senses the current flowing in the capacitance element or the inductance element and outputs an amplified current and a second current path for supplying the output current of the amplifier circuit to the LC resonance circuit are provided.
This constitution makes it possible to differentiate the Q factor by converting the voltage across the LC resonance circuit into a current and supplying the current via the first current path to the LC resonance circuit.
The oscillation frequency can also be differentiated by sensing the current flowing in the capacitance element or the inductance element and supplying the amplified current via the second current path to the LC resonance circuit.
The constitution of the fifth invention described above may also be modified so that the voltage-current converter circuit and the amplifier circuit differentiate the voltage-current conversion ratio and the amplification gain, respectively, in accordance with signals that are individually supplied thereto. Q factor can be differentiated by changing the voltage-current conversion ratio of the voltage-current converter circuit, and the oscillation frequency can be changed by changing the amplification gain of the amplifier circuit. Consequently, the oscillation frequency and the Q factor can be differentiated in accordance with signals supplied from the outside. The voltage-current conversion ratio of the voltage-current converter circuit and the amplification gain of the amplifier circuit may also be differentiated in accordance with each other. Such an operation scheme makes it possible to maintain the oscillation output substantially constant even when the oscillation frequency changes.
An oscillation circuit of the sixth invention comprises the main portion of oscillation circuit, the second and third transistor pairs, the second and third current sources, the first and second resistors, the connection means, a third resistor, a fourth transistor pair and a fourth current source.
The main portion of oscillation circuit comprises the first transistor pair, the LC resonance circuit and the first current source.
Emitters of the transistors of the first transistor pair are connected with each other, and the base of each transistor is connected to the collector of the other transistor. The LC resonance circuit is connected with the collectors of the transistors of the first transistor pair. The first current source is connected to the emitters of the transistors of the first transistor pair. The main portion of oscillation circuit outputs the oscillation signal at the collectors of the transistors of the first transistor pair.
Emitters of the transistors of the second transistor pair are connected with each other, and emitters of the transistors of the third transistor pair are connected with each other
The second current source is connected to the emitters of the transistors of the second transistor pair, and the third current source is connected to the emitters of the transistors of the third transistor pair.
The first resistor is connected, on one terminal thereof, to the junction of the collector and the base of one of the transistors of the second transistor pair and the base of one of the transistors of the third transistor pair.
The second resistor is connected, on one terminal thereof, to the junction of the collector and the base of the other transistors of the second transistor pair and the base of the other transistor of the third transistor pair.
The connecting means connects the other terminals of the first and the second resistors and the collectors of the transistors of the first transistor pair, respectively.
The third resistor senses the current flowing in the element that constitutes the LC resonance circuit.
Emitters of the transistors of the fourth transistor pair are connected with each other, and bases of the transistors are connected to terminal of the third resistor, while the collectors of the transistors are connected to the collectors of the transistors of the first transistor pair.
The fourth current source is connected to the emitters of the transistors of the fourth transistor pair.
This constitution makes it possible to differentiate the oscillation frequency of the main portion of oscillation circuit in accordance with the current ratio between the first and fourth current sources. Q factor can also be differentiated in accordance with the current ratio between the second and third current sources.
In the oscillation circuit of the sixth invention, such a constitution may also be employed as the value of current of the fourth current source is differentiated in accordance with a signal supplied from the outside, and the value of current of at least one of the second and third current sources is differentiated in accordance with a signal supplied from the outside
Such a constitution makes it possible to differentiate the current from the fourth current source in accordance with the signal supplied from the outside, thereby differentiating the frequency. Particularly in case such a PLL circuit is made as a signal of a predetermined frequency is output by comparing the phases of a signal of a reference signal source that provides output of a stable oscillation frequency and a signal of this oscillator, Q factor can be differentiated thus making it possible to maintain the oscillation output power and the C/N characteristic substantially constant, by supplying a signal that carries phase error information received from the PLL circuit to the fourth current source thereby differentiating the oscillation frequency and differentiating the currents supplied from the second and third current sources respectively.